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1 <?php 2 3 /** 4 * Class for converting between different unit-lengths as specified by 5 * CSS. 6 */ 7 class HTMLPurifier_UnitConverter 8 { 9 10 const ENGLISH = 1; 11 const METRIC = 2; 12 const DIGITAL = 3; 13 14 /** 15 * Units information array. Units are grouped into measuring systems 16 * (English, Metric), and are assigned an integer representing 17 * the conversion factor between that unit and the smallest unit in 18 * the system. Numeric indexes are actually magical constants that 19 * encode conversion data from one system to the next, with a O(n^2) 20 * constraint on memory (this is generally not a problem, since 21 * the number of measuring systems is small.) 22 */ 23 protected static $units = array( 24 self::ENGLISH => array( 25 'px' => 3, // This is as per CSS 2.1 and Firefox. Your mileage may vary 26 'pt' => 4, 27 'pc' => 48, 28 'in' => 288, 29 self::METRIC => array('pt', '0.352777778', 'mm'), 30 ), 31 self::METRIC => array( 32 'mm' => 1, 33 'cm' => 10, 34 self::ENGLISH => array('mm', '2.83464567', 'pt'), 35 ), 36 ); 37 38 /** 39 * Minimum bcmath precision for output. 40 * @type int 41 */ 42 protected $outputPrecision; 43 44 /** 45 * Bcmath precision for internal calculations. 46 * @type int 47 */ 48 protected $internalPrecision; 49 50 /** 51 * Whether or not BCMath is available. 52 * @type bool 53 */ 54 private $bcmath; 55 56 public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) 57 { 58 $this->outputPrecision = $output_precision; 59 $this->internalPrecision = $internal_precision; 60 $this->bcmath = !$force_no_bcmath && function_exists('bcmul'); 61 } 62 63 /** 64 * Converts a length object of one unit into another unit. 65 * @param HTMLPurifier_Length $length 66 * Instance of HTMLPurifier_Length to convert. You must validate() 67 * it before passing it here! 68 * @param string $to_unit 69 * Unit to convert to. 70 * @return HTMLPurifier_Length|bool 71 * @note 72 * About precision: This conversion function pays very special 73 * attention to the incoming precision of values and attempts 74 * to maintain a number of significant figure. Results are 75 * fairly accurate up to nine digits. Some caveats: 76 * - If a number is zero-padded as a result of this significant 77 * figure tracking, the zeroes will be eliminated. 78 * - If a number contains less than four sigfigs ($outputPrecision) 79 * and this causes some decimals to be excluded, those 80 * decimals will be added on. 81 */ 82 public function convert($length, $to_unit) 83 { 84 if (!$length->isValid()) { 85 return false; 86 } 87 88 $n = $length->getN(); 89 $unit = $length->getUnit(); 90 91 if ($n === '0' || $unit === false) { 92 return new HTMLPurifier_Length('0', false); 93 } 94 95 $state = $dest_state = false; 96 foreach (self::$units as $k => $x) { 97 if (isset($x[$unit])) { 98 $state = $k; 99 } 100 if (isset($x[$to_unit])) { 101 $dest_state = $k; 102 } 103 } 104 if (!$state || !$dest_state) { 105 return false; 106 } 107 108 // Some calculations about the initial precision of the number; 109 // this will be useful when we need to do final rounding. 110 $sigfigs = $this->getSigFigs($n); 111 if ($sigfigs < $this->outputPrecision) { 112 $sigfigs = $this->outputPrecision; 113 } 114 115 // BCMath's internal precision deals only with decimals. Use 116 // our default if the initial number has no decimals, or increase 117 // it by how ever many decimals, thus, the number of guard digits 118 // will always be greater than or equal to internalPrecision. 119 $log = (int)floor(log(abs($n), 10)); 120 $cp = ($log < 0) ? $this->internalPrecision - $log : $this->internalPrecision; // internal precision 121 122 for ($i = 0; $i < 2; $i++) { 123 124 // Determine what unit IN THIS SYSTEM we need to convert to 125 if ($dest_state === $state) { 126 // Simple conversion 127 $dest_unit = $to_unit; 128 } else { 129 // Convert to the smallest unit, pending a system shift 130 $dest_unit = self::$units[$state][$dest_state][0]; 131 } 132 133 // Do the conversion if necessary 134 if ($dest_unit !== $unit) { 135 $factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp); 136 $n = $this->mul($n, $factor, $cp); 137 $unit = $dest_unit; 138 } 139 140 // Output was zero, so bail out early. Shouldn't ever happen. 141 if ($n === '') { 142 $n = '0'; 143 $unit = $to_unit; 144 break; 145 } 146 147 // It was a simple conversion, so bail out 148 if ($dest_state === $state) { 149 break; 150 } 151 152 if ($i !== 0) { 153 // Conversion failed! Apparently, the system we forwarded 154 // to didn't have this unit. This should never happen! 155 return false; 156 } 157 158 // Pre-condition: $i == 0 159 160 // Perform conversion to next system of units 161 $n = $this->mul($n, self::$units[$state][$dest_state][1], $cp); 162 $unit = self::$units[$state][$dest_state][2]; 163 $state = $dest_state; 164 165 // One more loop around to convert the unit in the new system. 166 167 } 168 169 // Post-condition: $unit == $to_unit 170 if ($unit !== $to_unit) { 171 return false; 172 } 173 174 // Useful for debugging: 175 //echo "<pre>n"; 176 //echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n"; 177 178 $n = $this->round($n, $sigfigs); 179 if (strpos($n, '.') !== false) { 180 $n = rtrim($n, '0'); 181 } 182 $n = rtrim($n, '.'); 183 184 return new HTMLPurifier_Length($n, $unit); 185 } 186 187 /** 188 * Returns the number of significant figures in a string number. 189 * @param string $n Decimal number 190 * @return int number of sigfigs 191 */ 192 public function getSigFigs($n) 193 { 194 $n = ltrim($n, '0+-'); 195 $dp = strpos($n, '.'); // decimal position 196 if ($dp === false) { 197 $sigfigs = strlen(rtrim($n, '0')); 198 } else { 199 $sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character 200 if ($dp !== 0) { 201 $sigfigs--; 202 } 203 } 204 return $sigfigs; 205 } 206 207 /** 208 * Adds two numbers, using arbitrary precision when available. 209 * @param string $s1 210 * @param string $s2 211 * @param int $scale 212 * @return string 213 */ 214 private function add($s1, $s2, $scale) 215 { 216 if ($this->bcmath) { 217 return bcadd($s1, $s2, $scale); 218 } else { 219 return $this->scale((float)$s1 + (float)$s2, $scale); 220 } 221 } 222 223 /** 224 * Multiples two numbers, using arbitrary precision when available. 225 * @param string $s1 226 * @param string $s2 227 * @param int $scale 228 * @return string 229 */ 230 private function mul($s1, $s2, $scale) 231 { 232 if ($this->bcmath) { 233 return bcmul($s1, $s2, $scale); 234 } else { 235 return $this->scale((float)$s1 * (float)$s2, $scale); 236 } 237 } 238 239 /** 240 * Divides two numbers, using arbitrary precision when available. 241 * @param string $s1 242 * @param string $s2 243 * @param int $scale 244 * @return string 245 */ 246 private function div($s1, $s2, $scale) 247 { 248 if ($this->bcmath) { 249 return bcdiv($s1, $s2, $scale); 250 } else { 251 return $this->scale((float)$s1 / (float)$s2, $scale); 252 } 253 } 254 255 /** 256 * Rounds a number according to the number of sigfigs it should have, 257 * using arbitrary precision when available. 258 * @param float $n 259 * @param int $sigfigs 260 * @return string 261 */ 262 private function round($n, $sigfigs) 263 { 264 $new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1 265 $rp = $sigfigs - $new_log - 1; // Number of decimal places needed 266 $neg = $n < 0 ? '-' : ''; // Negative sign 267 if ($this->bcmath) { 268 if ($rp >= 0) { 269 $n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1); 270 $n = bcdiv($n, '1', $rp); 271 } else { 272 // This algorithm partially depends on the standardized 273 // form of numbers that comes out of bcmath. 274 $n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0); 275 $n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1); 276 } 277 return $n; 278 } else { 279 return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1); 280 } 281 } 282 283 /** 284 * Scales a float to $scale digits right of decimal point, like BCMath. 285 * @param float $r 286 * @param int $scale 287 * @return string 288 */ 289 private function scale($r, $scale) 290 { 291 if ($scale < 0) { 292 // The f sprintf type doesn't support negative numbers, so we 293 // need to cludge things manually. First get the string. 294 $r = sprintf('%.0f', (float)$r); 295 // Due to floating point precision loss, $r will more than likely 296 // look something like 4652999999999.9234. We grab one more digit 297 // than we need to precise from $r and then use that to round 298 // appropriately. 299 $precise = (string)round(substr($r, 0, strlen($r) + $scale), -1); 300 // Now we return it, truncating the zero that was rounded off. 301 return substr($precise, 0, -1) . str_repeat('0', -$scale + 1); 302 } 303 return sprintf('%.' . $scale . 'f', (float)$r); 304 } 305 } 306 307 // vim: et sw=4 sts=4
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